The invention encompasses method and apparatus for obtaining gas conditioning by low-temperature vaporization and compression of refrigerants. Modern refrigeration and air-conditioning systems are relatively unchanged from the original units developed in the late 1920's and early 1930's. Although some methods had been developed earlier, the modern industry began with the discovery of freon by Thomas Midgely and Charles Kettering in 1928. Freon is a chlorofluorocarbon that is ideally suited to refrigeration in simple systems because of its low boiling point and low heat of vaporization, in addition to its stability, nontoxicity, and nonflammability. These characteristics made freon and its variations the refrigerant of choice in most of the refrigeration units built to date, given the relatively inefficient means provided for vaporizing that refrigerant.
In many of these earlier systems, as little as half of the refrigerant was vaporized, resulting in a serious loss of efficiency. This unfortunate result was due to the limited opportunity afforded the refrigerant to absorb the heat necessary to change its liquid state to a vapor. In these systems, an evaporator coil was filled with liquid refrigerant and the pressure reduced as it passed through the expansion valve. By the time the refrigerant completed its tortuous path through the lengthy evaporator coil, vapor slowly began to form, heat was absorbed, and the gas compressed to pass through the cycle repeatedly. The remaining liquid was diverted by suction tubes to the high pressure side because it would damage the compressor if it passed through with the vapor. Conversion of as much of the refrigerant to vapor as possible is very important, because the change of state can result in thermal transfers up to 50 times as large as mere pressure changes alone. Any refrigerant that does not change "state" represents lost heat absorption potential.
The refrigeration systems of the past 60 years have accordingly been improved in various ways, including providing larger surfaces in heat exchangers, variable rate compressors, etc. but the basic operation of these units, which are dependent of chlorofluorocarbons (hereinafter CFC's) to overcome their inherent inefficiencies, have not. As long as freon continued to be available without restriction, there was little pressure to improve the process of vaporization because freon was "good enough." It allowed a multi-billion dollar industry to be established worldwide and did much to improve health and living standards everywhere. Unfortunately, environmental problems associated with their use have become so severe that the chlorofluorocarbon option will soon be unavailable.
The recent determination that CFC's are causing serious depletion of the critical ozone layer has led to a fundamental rethinking of out tolerance of CFC's as refrigerants. Because CFC's are such stable compounds, they eventually reach the upper atmosphere where they are bombarded by cosmic rays. This causes the molecular bonds to be broken, in turn freeing the chlorine atoms. Chlorine acts as a catalyst in the destruction of ozone(O.sub.3) molecules, even though it does not combine chemically with it. The ozone is reduced to normal oxygen (O.sub.2) by this catalytic action. One chlorine atom can destroy as many as 100,000 ozone atoms before it is returned to the surface in precipitation.
This is recognized as a serious problem because the ozone layer is an efficient reflector of harmful ultraviolet radiation from the sun. Without that layer, which has been thinning rapidly in direct response to the increased use of CFC's, even brief solar exposure to unprotected humans could result at the least in serious sunburn. Longer exposures could be life-threatening: including severe burns, skin cancer, and other negative health consequences.
CFC's are known to be 10,000 times more likely than CO.sub.2 to cause the "greenhouse effect", CFC's alone account for aproximately 20 percent of that problem. This undesirable effect is created by the retention in the atmosphere of heat energy by the CFC's CO.sub.2, and methane which, when combined, allow the incoming sunlight to pass through, but not the heat that is produced when the light is absorbed on the surface of the earth.
The ozone depletion problem has become so severe a threat to global health that it has become the object of the international treaty (the Montreal Protocol.) That treaty, to which the United States is signatory, is expected to reduce CFC production by 50 percent by the end of the 1990's. The EPA recently announced that the problem was so severe that by 1998 it would completely ban CFC's in the United States. As indicated above, several major CFC producers have already announced their intention to scale back CFC production and to eventually cease it completely. CFC's are obviously on their way out.
The refrigeration and air conditioning industries, however, clearly face major dilemma because of this phase out, as does the world in general, which is highly dependent on a CFC source of cooling for food preservation and human comfort. These industries, it is anticipated, will survive, along with living standards of much of the world, only if new refrigerants can replace known CFC's. Several possibilities exist, but the most promising is 134A, a nonchlorinated fluorocarbon. It meets the requirements of being environmentally benign, nontoxic, stable, Nonflammable, and affordable. 134A is, nevertheless, more difficult to convert from a liquid to a gas, because of its greater heat of vaporization and its high pressure range. In existing systems, 134A has not performed well and has not produced the temperature reductions that users need. Other potential refrigerants are even more difficult than 134A to vaporize and require more work to condense. Accordingly, the present invention addresses the adaptation of such refrigerant compounds as 134A and a wide variety of new refrigerants to function efficiently in such fields as air conditioning and heating.
It is apparent that the present new technological approach to refrigeration is needed. The principal reason that such technology has changed so little in the last 60 years is that there was no real social or economic pressure for it to change. As long as freon was acceptable as a refrigerant, inefficient and primitive systems considered to function adequately. Now that such easily vaporized materials will no longer be available, a fundamental system change in hardware becomes necessary to accommodate the new family of refrigerants which this system will make practical.
The heat pump apparatus and method defined hereinafter present that technological breakthrough. It is a substantial improvement in all, not just one or two, phases of the refrigeration cycle. It will allow the use of 134A or virtually any other potential refrigerant, all with higher optimum efficiency than exists in any existing system.
"Heat pump" herein comprises an engine or reversible engine, capable of functioning either as a producer of refrigeration or heat under the Carnot principle.